I'm looking for input on options to measure the number of rotations of a shaft using a esp32. The speed is less than 500 rpm. The direction of rotation is already known. I really only need 4 pulses per rotation. No matter which way I go I will need to machine the disk that has magnets, holes / slots or teeth to count. I'm leaning toward a A3144 hall effect sensor. The question I have with that option is the minimum voltage is 4.5v. Can this be used with the pull-up resister tied to 3.3V while the sensor is powered by 5v? The only critical consideration is that it needs to operate outdoors with a possible temperature swing of -35f to +130f.

 

I believe if you power it with 5V the output, with a pull-up resistor to pull the output high, the output will go low if it detects a magnet. If the high output is then reduced to 3.3V using a potential divider then I think it will be compatible with the processor

Rather than 4 magnets could you use a single magnet with a piece of soft iron completing the magnet circuit between two adjacent teeth of your 4 teeth wheel which will raise the magnetic field only when those two teeth are lined up with the ends of the soft iron?

 

I believe if you power it with 5V the output, with a pull-up resistor to pull the output high, the output will go low if it detects a magnet. If the high output is then reduced to 3.3V using a potential divider then I think it will be compatible with the processor

Rather than 4 magnets could you use a single magnet with a piece of soft iron completing the magnet circuit between two adjacent teeth of your 4 teeth wheel which will raise the magnetic field only when those two teeth are lined up with the ends of the soft iron?

If that pickup uses a coil and a magnet that would be a Variable Reluctance pickup which is available from quite a few sources and has the big advantage of not needing any electrical power. That makes it simpler to use.

 

If that pickup uses a coil and a magnet that would be a Variable Reluctance pickup which is available from quite a few sources and has the big advantage of not needing any electrical power. That makes it simpler to use.

That definitely gives me some more ideas. Thanks, can you point out any of those sources?

 

That definitely gives me some more ideas. Thanks, can you point out any of those sources?

I would start the search with Digikey, I am not sure if Automation Direct carries them that would be the less expensive source. It has been a long time since I ordered one of them.

 

https://www.phoenixamerica.com/products/gear-tooth/variable-reluctance.html

VR sensors are very robust, good for nasty environments that kill integrated sensors.

 

Depending on the environment, a simple solution might be a piece of reflective tape on the shaft and an optical sensor. Is there a place on the shaft where the tape can be mounted that will remain clean?

 

You have not specified some important details:

Does this need to work to zero speed?
Can you tolerate missed pulses?